According to Belinda Medlyn, a theoretical ­biologist with Western Sydney University, trees exposed to enhanced CO2, in the gigantic open air Hawkesbury River climate study, grow 35% faster than their neighbours in the control group.

“Either they’re getting more carbon for the same amount of water, or they’re getting the same amount of carbon but using less water.”

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Since 2012, the researchers have pumped extra CO2into three of six basketball court-sized rings of 80-year-old bush. This has raised the CO2 concentration in the three plots to about 550 parts per million, up from the ambient level of 400 ppm.

Measurements revealed that for each unit of water absorbed, the trees in the CO2-enriched rings reaped 35 per cent more carbon than the trees in the control plots.